This invention relates generally to a beaded conduit joint, sometimes referred to as “Marmon” conduit couplings, and more particularly to improved beaded couplings and methods for forming beaded couplings in conduit blanks.
Joining conduits is common in many products and systems, including vehicle engine exhaust systems. Beaded couplings (or “joints”) are used to connect two conduits or other components. Beaded couplings are well known and include a first conduit having an end portion on which an outwardly extending annular flange is formed, and a second conduit having a flared end for mating with the annular flange. Once fitted together, the two conduits are releasably joined using a clamp that engages both the annular flange and the flared end to secure the two conduits together.
Various modifications to beaded couplings are known that improve various aspects of the couplings, but they all face similar obstacles in the manufacturing process. For example, mating faces of the outwardly extending annular flange and the flared end must match well enough to resist leaking and other failures. Gaskets between mating faces and in the clamp can be used, but tolerances must still be tight and consistent in high-performance applications.
Known manufacturing techniques for forming beaded couplings can result in poor fits and leaks between conduits. This is especially true in high pressure and temperature applications, such as engine exhaust systems where tolerances are tight. For example, some forming methods result in annular flanges with irregular profiles, tooling marks on sealing faces, and excessive thinning of
Conduit material at the outwardly extending annular flange and at the flared end of the mating conduit.
The annular flange and the flared end were typically formed by using an indexing/sizing machine having a multi-hit ram that forms and sizes the annular flange on one piece and a flared end on a mating piece of the coupling. The ram can change the thickness of the material in the formed profile, and the parts typically are not formed to “full print geometry,” which is a term used to describe products with material extending fully into tight corners or recesses of forming dies. Such full print geometry products are difficult to obtain, especially with traditional index/sizing machines. Parts that do not have full print geometry may not be within manufacturing specifications and may even have wall thicknesses that are too thin because the wall material was stretched toward the extreme corners or recesses of the forming dies. To minimize the problems with thinning of the conduit wall material and related failures, the conduit walls are typically thick enough to compensate for the particular forming method being used, but the parts can still be outside of manufacturing tolerances when such manufacturing techniques are used. These prior manufacturing methods also leave noticeable tooling mark on the parts.
Additional complications in forming beaded couplings are apparent when one or both of the conduits is bent to form an elbow or is part of a component. In some situations to aid in manufacturing, a straight section of conduit is welded to an elbow after the beaded coupling elements are formed on a straight section. This additional step adds time and cost
Thus, there is a need for a beaded coupling manufacturing method that reduces tooling marks, minimizes flaws from conduit thinning, has consistent results, and can be used with elbow conduits or when other components are connected to the conduit in advance.